1. Technical Field
The invention relates to a method for determining non-uniformities of a loaded wheel, in particular a pneumatic motor vehicle wheel, such as variations of radial or lateral forces acting on the wheel or radial or lateral runout of the loaded wheel. Furthermore, the inventions relates to a system or an apparatus for carrying out such methods. In particular, the invention relates to an improved method and apparatus for contactless determination of said non-uniformities of a loaded wheel by simulating the loading.
2. Background Art
Even when a pneumatic motor vehicle wheel is balanced, non-uniformity in the construction of the tyre and also runout of the wheel rim can result in significant vibration forces when the wheel is rolling under load, what is the normal operation condition. The assumption that a wheel/tyre assembly which is suitably balanced under no-load condition will also be suitably balanced when installed on a vehicle and subjected to a substantial load resulting from the vehicle weight, is not necessarily valid.
Non-uniformities of a loaded wheel can result from radial or lateral runout of the tyre and/or the rim as well as variations in tyre stiffness caused by non-uniformities of tyre construction such as variations in the carcass or the tyre wall thickness, for example. Such non-uniformities cause variations in the rolling diameter of the loaded wheel along the circumference, i.e. within one revolution of the wheel. This results in vertical movements of the wheel axis, and thus vertical vibration forces acting on the wheel suspension of a driving vehicle.
It is desirable to determine said non-uniformities of a loaded wheel such as force variations and/or runout. Then the determined non-uniformities can be used during the operation of a wheel balancer or a tyre changer to correct the magnitudes or locations of balancing weights or to identify an angular remount position of the rim/tyre assembly, for example. Thus, disadvantageous effects of said non-uniformities of a loaded wheel can be mitigated or even eliminated.
A wheel balancer for determining non-uniformities such as radial force variations or radial runout of rolling loaded wheels is known from U.S. Pat. No. 6,397,675. With this wheel balancer, a load roller is provided for applying a substantial radial force to the rim/tyre assembly (wheel) during rotation of the wheel. Movement of the load roller during rotation of the wheel is observed to measure radial runout of the loaded wheel. Furthermore, vibration forces of the rolling loaded wheel are measured by the vibration sensors of the wheel balancer.
Providing a load roller to measure loaded rolling wheels under realistic conditions requires massive construction of a corresponding measuring apparatus because of the strong forces typically applied to the wheel by the load roller. This results in a heavy and bulky apparatus and increases costs.
It is an object of the present invention to provide an improved method and system for determining non-uniformities of a loaded wheel without requiring application of strong forces to the wheel.